MESA, Ariz. — The A’s clubhouse is emptying out. Many of the lockers have blank name tags above them. There’s tons of vacant space for some of the veterans to stretch out. The camp roster is down to 37.

The A’s optioned Paul Blackburn on Sunday, followed by Daniel Mengden on Monday. The decision to option Blackburn wasn’t much of a surprise. He missed a large chunk of the season last year with a right elbow injury. And in the 27 2/3 innings he pitched in 2018, Blackburn posted a 7.16 ERA. This spring, Blackburn threw eight innings, striking out seven and allowing only two earned runs over that span, but it never seemed like he was a legitimate contender for a rotation spot to open the season.

At least on the surface, it seemed like Mengden had a better shot. Last season, aside from a tumultuous June followed by a foot injury, he made an impression and adjusted well to the opener role once the A’s started employing that tactic. Now, he...